1. Field of the Invention
The present invention pertains to an integral omniphobic grout additive which can be added to grout prior to grout application, and which renders grout resistant to staining.
2. Description of the Related Art
Mineral-based cementitious grouts have been used for millennia. Grouts are widely used to fill the spaces between ceramic tiles and other surfacing materials in bathrooms, kitchens, and other areas, for example on diverse substrates as automobile repair floors and on dining tables with tile or stone surfaces. These grouts contain a mineral binder such as a hydraulically setting mineral material. Cementitious, lime-based, and gypsum-based grouts are all well known. In addition to the mineral binder, grouts commonly contain fillers such as sand, ground limestone, etc., as well as pigments, processing additives, and the like. Grouts are available in dry, “redi-mix” form from numerous manufacturers and suppliers.
A common problem with such grouts is their general inability to resist staining. When the grout is contacted by a staining material, the color and/or surface texture may be locally altered, presenting an unaesthetic appearance. Common stains include oils, greases, food products, and the like. Noteworthy is that some of these staining materials are hydrophilic, while others are hydrophobic. Some, like tomato ketchup, are highly colored, while others, such as vegetable oils, are practically colorless. For example, oil-stained grout may show little color change per se, but may appear darker than surrounding unstained areas. Staining materials may also be in the form of emulsions or dispersions such as mustard or ketchup, solutions (e.g. black coffee), combinations of these, or may be neat (e.g. oils, brake fluid, etc.). The staining constituents themselves may be organic, inorganic, or both. When the staining material is organic, the possibility of accelerated microbial growth, which may cause additional staining, is possible.
It would be desirable to provide a means of preventing staining of grout. In the past, two approaches to imparting stain resistance have been used.
In a first method, grout is applied conventionally, generally with the aid of a “float,” is then “tooled”, and finally excess grout adhering to tile surfaces is removed using a wet or damp cloth or sponge, generally after partial cure. Following cure (setting) of the grout, an external or “topical” stain repellant formulation is applied. The stain repellant may be a solution or dispersion of silicones, silanes, and/or fluorochemicals, for example. This approach to stain repellency has the disadvantage that additional, labor-intensive application is necessary, and the further disadvantage that penetration of the stain repellant into the grout is minimal; only the surface and near-subsurface areas are affected. Moreover, the stain repellant may be removed over the course of time, then requiring a further application of stain repellant. Homeowners, in particular, generally do not apply further stain repellant, even though needed.
The number of patents directed to topically applied water and/or oil repellants is evidence of the importance of preventing water ingress and/or staining. Representative examples include U.S. Pat. No. 5,399,191, which discloses topical oil and water repellant compositions in the form of an aqueous dispersion of a salt of an amino-functional silicone together with an alkylalkoxysilane. The compositions have little stain repellency, and suffer from the drawbacks of other topical compositions. U.S. Pat. No. 5,527,931 discloses an aqueous dispersion for topical application to also provide water and oil repellency. The active ingredient is a monosilane or siloxane bearing three different groups: a hydrophilic group, a hydrophobic group, and an oleophobic group. These compounds are expensive to prepare.
WO 2007/127267 A2 discloses external stain, water, and oil repellant compositions. The active ingredients include a fluoropolymer and one or more organosilicon compounds, which may be alkoxysilanes or polydiorganosiloxanes. The composition is solvent-borne. Volatile organic solvents are highly disfavored due to environmental (greenhouse gas) concerns. French patent publication FR 2639353 A discloses external aqueous masonry protectants containing a major proportion of a polymer latex, a fluoropolymer latex, an organosilicon compound or polyolefin wax dispersion, a water soluble stabilizer such as a glycol, and a water insoluble coalescing agent such as a glycol diether. U.S. Pat. No. 6,410,626 discloses aqueous dispersion for external application to building materials for imparting waterproofing properties. The compositions contain a repellant which may be a fluoropolymer surfactant, fluorine-substituted oil, or fluoroalkyl-substituted organopolysiloxane; a linear organopolysiloxane terminated with alkoxy groups and bearing pendent alkoxy groups on each siloxy silicon atom, or a trialkoxysilane; and a fluoro-substituted polyolefin resin such as PTFE.
U.S. Pat. No. 8,455,585 discloses an external aqueous waterproofing composition containing a polybutene polymer, a polyorganosiloxane, and surfactant, for use in application to wood and masonry.
The second method for providing stain repellency is to admix a stain repellent with the grout prior to application to the tile or other surface. Such stain repellant additives are “integral” stain repellants. However, although such stain repellant additives are available, their stain-resisting performance is low. In addition, some additives may alter the setting properties of the grout, including “work time” or “open time,” or may reduce physical properties of the cured grout to unacceptably low levels. For example, the grout may no longer be able to meet minimum ANSI standards. Also, some additives interfere with the ability to remove excess grout from stone or tile surfaces. Finally, the stain repellant additive must be economical.
Alkyl orthosilicates such as tetraethylsilicate and alkali metal organosiliconates have long been added to mineral construction materials such as plasters, renders, and cements to increase water repellency. However, these additives do little to protect against staining, and even their water repellant properties leave much to be desired.
U.S. Pat. No. 7,875,674 discloses the addition of a hydrophobic silicone resin into a curable inorganic matrix such as cement, followed by autoclaving at a temperature higher than the melting temperature of the silicone resin. No indication of any stain resistance is disclosed. The compositions are for reducing water ingress to prevent freeze/thaw damage. Grout cannot be autoclaved at high temperature. In the past, curable epoxy resins have also been added during mixing of grout, sometimes with further stain repellant ingredients. However, the grout then has only a small working time (short “pot life”), and stain repellency is still relatively low.
It would be desirable to provide an integral grout additive which can be easily admixed with other grout components during grout preparation; which is effective to minimize staining by divergent types of stains, including both hydrophilic (aqueous) and oleophilic (oily) stains (“omniphobic”); which maintains grout workability and physical properties, and which does not interfere with conventional grout application and cleanup.